Sharp R-757M (serv.man17) Service Manual ▷ View online
R-757M - 13
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two
terminals as described in the table below.
terminals as described in the table below.
L (min)
Cx
±
20%
Cy
±
20%
1.0mH
0.22
µ
F
4700pF
MEASURING POINTS
INDICATION OF OHMMETER
Between N and L
Approx. 680 k
Ω
Between terminal N and WHITE
Short circuit
Between terminal L and RED
Short circuit
If incorrect readings are obtained, replace the noise filter unit.
CARRY OUT 4R CHECKS.
I
NOISE FILTER TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of
noise filter.
Using an ohmmeter, check between the termi-
nals as described in the following table.
noise filter.
Using an ohmmeter, check between the termi-
nals as described in the following table.
J
MOTOR WINDING TEST
Table: Resistance of Motor
Motors
Resistance
Fan motor
Approximately
290
Ω
Turntable motor
Approximately 14.6 k
Ω
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
RED
WHT
L
L
R1
L
R2
N
Cx
Cy
20A
R1: 10M ohm
±
20%
R2: 680k ohm
±
20%
F8A
K
GRILL HEATING ELEMENT TEST
CARRY OUT 3D CHECKS.
Before carrying out the following tests make sure the heating element is cooled completely.
1. Resistance of heating element.
Disconnect the wire leads to the heating element to be tested. Using ohmmeter with low resistance
range. Check the resistance across the terminals of the heating element as described in the
following table.
range. Check the resistance across the terminals of the heating element as described in the
following table.
Table: Resistance of heating element
Parts name
Resistance
Grill heating element
Approximately 61
Ω
2. Insulation resistance.
Disconnect the wire leads to the heating element to be tested. Check the insulation resistance
between the element terminal and cavity using a 500V - 100M
between the element terminal and cavity using a 500V - 100M
Ω
insulation tester. The insulation
resistance should be more than 10 M
Ω
in the cold element.
If the results of above test 1 and/or 2 are out of above specifications, the heating element is probably
faulty and should be replaced.
faulty and should be replaced.
CARRY OUT 4R CHECKS.
R-757M - 14
N
RELAY TEST
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable
is making good contact, verify that the stop switch operates properly; that the contacts are closed when
the door is closed and open when the door is open. If the stop switch is good, press stop/clear pad while
checking continuity between pins 5 and 12 of connector CN-G. If no continuity is measured, the key
unit is faulty and should be replaced. If continuity is measured, the control unit is faulty and should be
replaced. If a specific pad does not respond, the above method may be used. Disconnect the flat
ribbon cable that connects the key unit to the control unit and make sure the stop switch is closed (either
close the door or short the stop switch connector). Use the Key unit matrix indicated on the STOP/
CLEAR pad making momentary contact. If the control unit responds by clearing with a beep the key
unit is faulty and must be replaced. If the control unit does not respond, it is a faulty and must be
replaced. If a specific pad does not respond, the above method may be used (after clearing the control
unit) to determine if the control unit or key pad is at fault.
is making good contact, verify that the stop switch operates properly; that the contacts are closed when
the door is closed and open when the door is open. If the stop switch is good, press stop/clear pad while
checking continuity between pins 5 and 12 of connector CN-G. If no continuity is measured, the key
unit is faulty and should be replaced. If continuity is measured, the control unit is faulty and should be
replaced. If a specific pad does not respond, the above method may be used. Disconnect the flat
ribbon cable that connects the key unit to the control unit and make sure the stop switch is closed (either
close the door or short the stop switch connector). Use the Key unit matrix indicated on the STOP/
CLEAR pad making momentary contact. If the control unit responds by clearing with a beep the key
unit is faulty and must be replaced. If the control unit does not respond, it is a faulty and must be
replaced. If a specific pad does not respond, the above method may be used (after clearing the control
unit) to determine if the control unit or key pad is at fault.
M
KEY UNIT TEST
L
TOUCH CONTROL PANEL ASSEMBLY TEST
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc.
Therefore, unlike conventional microwave ovens, proper maintenance cannot be performed with
only a voltmeter and ohmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit and
Key Unit, and also the control unit is divided into two units, CPU Unit and Power Unit, and
troubleshooting by unit replacement is described according to the symptoms indicated.
1. Key Unit
Therefore, unlike conventional microwave ovens, proper maintenance cannot be performed with
only a voltmeter and ohmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit and
Key Unit, and also the control unit is divided into two units, CPU Unit and Power Unit, and
troubleshooting by unit replacement is described according to the symptoms indicated.
1. Key Unit
The following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
2. Control Unit
The following symptoms indicate a defective control unit. Replacing the control unit.
2-1 In connection with pads.
a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.
b) When touching the pads, no pads produce a signal.
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible problems caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
b) Clock does not operate properly.
c) Cooking is not possible.
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
G12
G11
G10
G 9
G 1
G 2
G 3
G 4
G 5
G 6
G 7
G 8
ROAST BEEF / LAMB
WHOLE POULTRY
CHICKEN QUARTERS
ROAST PORK
PASTA DISH
RISOTTO
GRATIN
MEAT JOINT
ROAST POULTRY
MICROWAVE
POWER LEVEL
GRILL
DOWN
LESS
MORE
UP
KITCHEN
TIMER
CLEAR
AUTO MINUTE
STOP
START
DELAY START
CLOCK SET
KG / LB
CONVERSION
AUTO
COOK
DUAL GRILL
1. CARRY OUT 3D CHECKS.
2. Disconnect the leads from the primary of the high voltage transformer. Make sure that the leads
2. Disconnect the leads from the primary of the high voltage transformer. Make sure that the leads
remain isolated from other oven components and chassis. (Use insulation tape if necessary.)
R-757M - 15
To protect the electronic circuits, this model is provided with a fine foil pattern added to the primary
on the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting
guide given below for repair.
on the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting
guide given below for repair.
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.
STEPS
OCCURANCE
CAUSE OR CORRECTION
The rated AC voltage is not present at
1
POWER terminal of CPU connector (CN-A).
Check supply voltage and oven power cord.
The rated AC voltage is present at primary
Low voltage transformer or secondary circuit defective.
2
side of low voltage transformer.
Check and repair.
*Insert jumper wire J1 and solder.
3
Only pattern at "a" is broken.
(CARRY OUT 3D CHECKS BEFORE REPAIR)
*Insert the coil RCILF2003YAZZ between "c" and "d".
4
Pattern at "a" and "b" are broken.
(CARRY OUT 3D CHECKS BEFORE REPAIR)
NOTE: *At the time of these repairs, make a
visual inspection of the varistor for burning
damage and examine the transformer with
tester for the presence of layer short-
circuit (check primary coil resistance). If
any abnormal condition is detected,
replace the defective parts.
damage and examine the transformer with
tester for the presence of layer short-
circuit (check primary coil resistance). If
any abnormal condition is detected,
replace the defective parts.
CARRY OUT 4R CHECKS.
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
3. Close the door.
4. Reconnect the supply.
5. Check the voltage between Pin Nos. 1 and 3 of the 3 pin connector (A) on the control unit with
4. Reconnect the supply.
5. Check the voltage between Pin Nos. 1 and 3 of the 3 pin connector (A) on the control unit with
an A.C. voltmeter. The meter should indicate 230-240 volts, if not check oven circuit.
6. RY1, RY2 and RY3 TEST
These are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during the
These are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during the
microwave cooking operation, grill cooking or dual grill cooking operation.
DC. voltage indicated .............. Defective relay.
DC. voltage not indicated ........ Check diode which is connected to the relay coil. If diode is good,
DC. voltage not indicated ........ Check diode which is connected to the relay coil. If diode is good,
control unit is defective.
RELAY SYMBOL
OPERATIONAL VOLTAGE
CONNECTED COMPONENTS
RY1
APPROX. 18.0V D.C.
Oven lamp / Turntable motor / Cooling fan motor
RY2
APPROX. 24.0V D.C.
Grill heating element
RY3
APPROX. 18.0V D.C.
High voltage transformer
O
PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING
BOARD (PWB) IS OPEN
BOARD (PWB) IS OPEN
CN - A
AC
31
VRS1
(J1)
a
c
d
b
R-757M - 16
The touch control section consists of the following units.
(1) Key Unit (The key unit consists of a FPC membrane
and a Graphic sheet.)
(2) Control Unit (The Control Unit consists of Power
Unit and CPU Unit).
The principal functions of these units and the signals
communicated among them are explained below.
communicated among them are explained below.
Key Unit
The key unit is composed of a matrix, signals generated
in the LSI are sent to the key unit through P20, P21,
P22, P23, P24, P25, P26 and P27.
When a key pad is touched, a signal is completed
through the key unit and passed back to the LSI
through P43, P44, P45 and P46 to perform the function
that was requested.
The key unit is composed of a matrix, signals generated
in the LSI are sent to the key unit through P20, P21,
P22, P23, P24, P25, P26 and P27.
When a key pad is touched, a signal is completed
through the key unit and passed back to the LSI
through P43, P44, P45 and P46 to perform the function
that was requested.
Control Unit
Control unit consists of LSI, ACL circuit, indicator circuit,
power source circuit, relay circuit, buzzer circuit,
synchronizing signal circuit and back light circuit.
Control unit consists of LSI, ACL circuit, indicator circuit,
power source circuit, relay circuit, buzzer circuit,
synchronizing signal circuit and back light circuit.
1) ACL
This circuit generates a signal which resets the LSI
to the initial state when power is supplied.
to the initial state when power is supplied.
2) Indicator Circuit
This circuit consists of 4-digits, 12-segments and 3
common electrodes using a Liquid Crystal Display.
common electrodes using a Liquid Crystal Display.
TOUCH CONTROL PANEL ASSEMBLY
OUTLINE OF TOUCH CONTROL PANEL
3) Power Source Circuit
This circuit generates voltages necessary in the
control unit from the AC line voltage.
In addition, the synchronizing signal is available in
order to compose a basic standard time in the clock
circuit.
control unit from the AC line voltage.
In addition, the synchronizing signal is available in
order to compose a basic standard time in the clock
circuit.
Symbol
Voltage
Application
VC
-5.2V
LSI(IC1)
4) Relay Circuit
A circuit to drive the magnetron, grill heating
element, fan motor, turntable motor and light the
oven lamp.
element, fan motor, turntable motor and light the
oven lamp.
5) Buzzer Circuit
The buzzer is responsive to signals from the LSI to
emit audible sounds (key touch sound and
completion sound).
emit audible sounds (key touch sound and
completion sound).
6) Synchronizing Signal Circuit
The power source synchronizing signal is available
in order to compose a basic standard time in the
clock circuit.
It accompanies a very small error because it works
on commercial frequency.
in order to compose a basic standard time in the
clock circuit.
It accompanies a very small error because it works
on commercial frequency.
7) Stop Switch
A switch to “tell” the LSI if the door is open or closed.
8) Back Light Circuit
A circuit to drive the back light (Light emitting diodes
LD1- LD5).
LD1- LD5).
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